Notify Operator when scene property update
here is how i did it in my addon, i registerd my property's in directly in the register def and made a def at the top of my script that gets called when the value of the property changes

def Update_BoolProp(self, context):
    pass
bpy.types.Object.BoolProp = bpy.props.BoolProperty(
    name="BoolProp",
    description="description",
    default = True,
    update = Update_BoolProp
    )


i think that you can define the update function where ever you like as long as you can access where you define your property's.  

ps: your vids are really helpful